1. Field of the Invention
The present invention relates to a process for etching semiconductor wafers by exposure to an etching mixture which is obtained by mixing nitric acid and hydrofluoric acid and optionally a surfactant.
2. The Prior Art
Semiconductor wafers, such as, silicon semiconductor wafers, as a base material for electronic components are obtained from a rod-shaped single crystal via a sequence of machining steps. First, the single crystal is cut into wafers. The near-surface crystal regions of the resultant semiconductor wafers are damaged to a depth of approximately 80 .mu.m by the wire or annular saws. This so-called "damage" is reduced, as a rule, by a mechanical surface treatment, for example by lapping or grinding the wafers. Wet-chemical removal of further silicon layers then results in almost complete removal of the damage. It also results in the deliberate production of defined surface parameters, such as microroughness and reflectivity. The object of etching is to obtain a wafer surface which is as plane-parallel and as defect-free as possible and which has a low microroughness and high reflectivity. If the etching process is performed in an acidic medium, nitric acid is frequently used as oxidizing agent and hydrofluoric acid is used as a dissolving agent, optionally in conjunction with a surfactant. An example of this type of etching process is described, in U.S. Pat. No. 5,451,267.
If these acids are used, the disposal of them as waste must be environmentally compatible. This waste disposal therefore generates substantial costs.